PURPOSE: To prevent the lowering of torque which is generated when the current consumption is reduced, by providing a controlling circuit, a rotation detecting circuit, and a voltage dropping circuit.

CONSTITUTION: A power source 8 is used as a power source, and a pulse width which can drive a step motor 11 actually is given to pulses, which are generated at intervals of a certain time in an oscillating and frequency dividing circuit 9, by a waveform synthesizing circuit 10, and it is discriminated in a controlling circuit 12 whether they are normal driving pulse or redriving pulses. In case of normal driving pulses, the power source 8 is so controlled that a voltage dropped by a voltage dropping circuit 14 is supplied to a driving circuit 13 of the next stage. After the step motor 11 is driven, rotation or non-rotation is detected by a rotation detecting circuit 15, and the operation is continued in case of rotation; but, in case of non-rotation, redriving pulses are generated, and the power source 8 is so controlled that the voltage of redriving pulses is directly driven by a high voltage from the power souce 8 which does not pass through the voltage dropping circuit 14, and thus, a value equal to or higher than the conventional value is secured for the output torque even if the current consumption is reduced.